Peri-Tetracene from 1,1-Bitetracene: Zipping up Structurally Defined Graphene Nanoribbons

Polycyclic aromatic hydrocarbons (PAHs) are promising molecules for a manifold of applications in organic electronics, spintronics, or energy storage devices. Among PAHs, particular attention has been focused on the synthesis and study of acenes and fused acenes, peri-acenes, allowing tuning of the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap with the size of the conjugated system. As a starting point for the surface synthesis of larger PAHs, we synthesized a 1,1 '-bitetracene for the first time. This precursor molecule consists of two tetracene units connected via the 1,1 '-position with a torsion angle of 70 degrees. The interface properties of the molecule before and after annealing on a Cu(111) surface are investigated. Using X-ray photoemission spectroscopy (XPS), angle-resolved photoelectron spectroscopy (ARPES), low-energy electron diffraction (LEED), and scanning-tunneling microscopy (STM), it is experimentally demonstrated that the tetracene units zip up with the help of heat forming peri-tetracene. These results and the exact adsorption geometry are in excellent agreement with calculations using density functional theory (DFT). Moreover, the calculations enable the identification of newly formed valence band states at the interface to Cu(111).